1. Field of the Invention
The present invention relates generally to a cylindrical vibration damping device usable as suspension bushings, engine mounts, body mounts, differential mounts, sub-frame mounts and the like, and more particularly to a cylindrical vibration damping device of fluid-filled type, which is capable of exhibiting vibration damping effects on the basis of flow action of non-compressible fluid sealed in a fluid sealing region enclosed therein, and which includes a stop rubber member installed within the fluid sealing region.
2. Description of the Related Art
A fluid filled cylindrical vibration damping device is known as one type of vibration damping couplings or mounts interposed between two components connected together in a vibration-isolating fashion. Disclosed in Citation 1 or 2 (see a document list in paragraph 0008) is an example of such a fluid-filled cylindrical vibration-damping device including an elastic rubber member elastically connecting a metallic inner shaft member, and a metallic outer sleeve member disposed about the inner shaft member, and a fluid sealing region defined between the inner shaft member and the outer sleeve member. When subjected to vibration applied thereto, the known fluid-filled cylindrical vibration-damping device is able to provide a vibration damping effect on the basis of flow action of non-compressible fluid sealed in the sealing region.
In the above-described known cylindrical vibration damping device, a stopper mechanism utilizing a stop rubber member, protruding from one of the inner shaft member and the outer sleeve member toward the other, is suitably installed in order to limit an amount of elastic deformation of the rubber elastic body in a cushion like manner during input of an excess vibrational load in its axial direction. Typically, the stop rubber member is disposed within the fluid-sealing region, as shown in the above-mentioned Citations 1 and 2, in order to avoid enlargement of the device itself.
However, the conventional stopper mechanism suffers from the inherent problem. Namely, in the event where the stopper rubber member comes into abutting contact at its projecting end portion with the inner shaft member or the outer sleeve member as a result of exertion of an excess external force thereon, a so-called “stick-slip” motion in boundary lubrication may occur in association with the elastic deformation of the stop rubber member. Accordingly, the conventional stop mechanism is prone to induce noises due to friction of the stop rubber member associated with its elastic deformation. Where the stop rubber member is installed in the fluid-sealing region, especially, the induced noises may be transmitted to the rubber elastic body via the sealed non-compressible fluid, and then amplified, so that the generation of noises becomes a significant problem. If a grease or other lubricant is applied to an abutting surface of the stop rubber member to minimize or reduce the noises, the grease is readily dispersed into the non-compressible fluid, making it difficult for the conventional stopper mechanism to provide effective noise damping performance.
To cope with this problem, there has been proposed another stopper mechanism wherein a rigid stop block is employed instead of the stop rubber member, and only a thin stop rubber layer is only formed secured on the a top abutting surface of the stop block, as disclosed in Citations 3 and 4, for example. Since the rigid stop block of the aforesaid structure permits a small amount of elastic deformation thereof upon abutting contact with the inner shaft or outer sleeve member, stick-slip motion at the abutting surface of the rigid stop block is prevented, making it possible to eliminate or minimize generation of the noises.
In the proposed stopper mechanism employing the rigid stop block, however, abutting noises and impact created as a result of abutting contact of the rigid stop block against the inner shaft or outer sleeve member cannot be absorbed only by means of the thin stop rubber layer. Therefore, the proposed stopper mechanism is very likely to suffer from the problem of abutting noises and impact induced upon abutting contact of the rigid stop block against the member. Moreover, the abutting contact of the rigid stop block may cause considerable change of spring characteristics of the vibration-damping device, making it impossible for the device to exhibit moderate load-spring characteristics.
[Citation 1]                JP-A-3-9138        
[Citation 2]                JP-B-3-30736        
[Citation 3]                JP-A-4-160244        
[Citation 4]                JP-U-1-149044        